A printing unit includes a blanket cylinder, an impression cylinder, an inking unit and optionally a damping unit. In the case of dry offset printing, for example, the damping unit is not necessarily a part of the printing unit.
Automatic washing devices are known for inking units, blanket cylinders and printing cylinders of a printing unit of an offset printing machine, which make rapid cleaning possible from a control desk--e.g., "Roland 700" brochure from MAN Roland Druckmaschinen AG. Using such a washing device, it is possible for a plurality of washing programs to be defined, which allow the device to adapt to different production conditions and to changes in the water and detergent. The washing operation is initiated manually from the control desk. Although this approach functions well, there remains a problem of how one of the washing programs is activated optimally or how a washing operation is to be initiated.
Furthermore, it is known to use a controlled supply of detergent for cleaning cylinders of a rotary printing machine, which ensures an approximately identical degree of moisture at the beginning of washing in the case of a washing roll or a washing cloth (DE 44 43 357, which is hereby incorporated herein by reference). To this end, the number of sheets printed since a previous washing are ascertained at the beginning of a washing operation. Depending on the number, the quantity of cleaning fluid--detergent and water--is to be supplied under control to the washing device. The number of washing operations is controlled with the same dependency. Although this approach works well, the quality of the cleaning could be improved.
In another example of an arrangement for cleaning a cylinder of a rotary printing machine, a washing device is thrown onto and off the cylinder. A washing roll or washing cloth is sprayed with the cleaning fluid. The detergent feed on the outer surface of the cylinder is controlled whilst taking into account the rotational speed and direction of rotation of the cylinder to be cleaned (DE 44 43 356). Although this approach also works well, the quality of the cleaning could be improved.